<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>验证用户名和密码</title>
</head>
<body>
    <script>
    var username = 'admin';
    var password = '123456';
    var flag =false;

     while( flag === false){
        var inputUsername = prompt('请输入用户名');
        var inputPassword = prompt('请输入密码');
        if(inputUsername === username && inputPassword === password) {
            alert('登陆成功');
            flag =true;
        }else {
            alert('用户名或者密码错误');
        }
     }

    </script>
</body>
</html>